Allergic reactions to tattoo pigments are fairly uncommon except for certain brands of red and green (with which some many people have a slight problem with itching, swelling, redness of the skin, oozing). People who are sensitive or allergic to certain metals may react to pigments in the skin by becoming swollen and/or itchy, oozing of clear sebum is also common. People with allergies should think carefully about getting a tattoo because of the risk of anaphylactic shock (hypersensitive reaction), which can be life threatening. Some tattoo artists give small tests, by marking a small amount of ink behind the ear to determine if that person has an allergic reaction.